Therefore, the present invention is based on the object of improving a device of the type named above in such a manner that before being provided to a processing device the glass melt is freed as much as possible of flaws such as cloudiness due to mini-particles, gas bubbles, streaks, discoloration and color deviation due to combustion products, and variations in thickness that remain permanently visible in the glass.
According to the present invention, this object is achieved in that
(a) between the melting region and the beginning of the refining region, there is situated a refining bench whose upper side has a distance from a constructively prespecified filling level of the glass melt such that a back-flow of the glass melt from the refining region to the melting region is as small as possible,(b) in each side wall, side burners and extraction openings for flue gases are situated between the at least one loading opening and the refining bench,(c) the constriction is delimited at both ends by end walls that leave open narrow flow cross-sections for flue gases above the glass melt, and(d) cooling means for the glass melt are situated inside the constriction.
Through the interaction of these means, the object of the invention is achieved reliably and economically in that the device of the type described above is improved such that before being supplied to a further processing device the glass melt is freed as much as possible of flaws such as cloudiness due to mini-particles, gas bubbles, streaks, discoloration and color deviation due to combustion products, and variations in thickness that remain permanently visible in the glass. Due to the refining bench and its blocking effect, back-flows into the melting region with strong heating, and the carrying along of disturbing effects, such as in particular particles, into the final product are prevented, and at the same time the energetic degree of efficiency is significantly improved, while protecting the environment.
The term “refining bench” was introduced by applicant several years ago because it indicates the geometry, spatial form, and relative position within the melt that a refining bench has. In the dictionary “ABC Glas” (Deutsche Verlag für Grundstoffundustrie, Leipzig, 1991), the terms “refining” and “refining zone” are explained on pages 165 and 166. According to page 165, what is concerned is a removal of bubbles by shortening the path of the bubble rise by causing a melt containing bubbles to flow slowly and horizontally in the take-off direction in a broad thin layer at a high temperature, e.g. over a floor wall installed in the melt. The shortening of the bubble rise path contributes here to the thermal refining effect. This principle ensures a strong refining effect (direct quotation). Similar statements can be found under the entry “refining zone” on page 166.
In further embodiments of the device, it is particularly advantageous if (either individually or in combination):                the cooling means are situated in the constriction in height-adjustable fashion,        the cooling means are made up of pipe segments whose axes are situated in meander-shaped fashion in a common vertical plane,        agitating elements are situated after the cooling means in the direction of flow,(a) between the at least one loading opening and the first flue gas extraction openings, there are situated side burners for the heating and melting of the glass raw materials, and(b) between the first flue gas extraction openings and the second flue gas extraction openings, there are situated further side burners for the completion of the melting, and in addition(c) the refining region is kept free of burners,        in the conditioning region, flue gas extraction openings and burners are situated in a sequence such that the flue gases flow in the direction opposite to the surface flow of the glass melt,        the floor surfaces are delimited from one another by a step formation that is fashioned so as to rise in the direction toward the overflow, in particular if the step height in each case is between 5 and 30 cm,        the difference in height of the floor surfaces before and after the refining bench is between 10 and 30 cm,        the level of filling of the glass melt over the refining bench is between 0.2 and 0.5 m, preferably between 0.3 and 0.4 m,        the length of the refining bench in the direction of the sum flow of the glass melt is between 0.8 and 3.0 m, preferably between 1.0 and 2.5 m,        the width of the melting region and refining region is between 6.0 and 10.0 m,        the ratio of the tub lengths inside the melting region (2) and the refining region before and after the refining bench is between 2.4 and 3.0,        the width ratio of the refining region to the constriction is between 0.4 and 0.6,        at least one preheating device for preheating oxidants for the combustion of the fuels is situated before the melting region,        the at least one preheating device is made up of a regenerator block, and/or        the melting device is fashioned as a cross-flame oven, if a respective generator block is situated on each side of the melting region and is connected via burner ports to the chamber above the glass melt, and if under-port burners are situated under the burner ports and above the surface of the glass melt.        
The present invention also relates to a method for producing a glass melt by means of a melting device having a loading opening for glass raw materials, the glass melt being conveyed to a final processing stage through a row arrangement of a melting region, a refining region, a constriction, a conditioning region, and an overflow.
In order to achieve the same object and the same advantages, such a method is characterized in that the glass melt
(a) is guided between the melting region and the refining region over a refining bench whose upper side has a distance from the filling level of the glass melt such that a back-flow of the glass melt from the refining region to the melting region is as small as possible,(b) is heated between the at least one loading opening and the refining bench by side burners and associated extraction openings for flue gases,(c) is cooled in the constriction by cooling means, and(d) is heated in the conditioning region by burners and flue gas extraction openings that are situated in a sequence such that the flue gases flow in the direction opposite to the surface flow of the glass melt,(e) the heat input dosage to the flow path of the glass melt being set such that the maximum temperature of the glass melt is reached above the refining bench.
In further embodiments of the method, it is particularly advantageous if (either individually or in combination):                the flow speed of the melt over the refining bench is set by cooling means that are situated in the constriction in height-adjustable fashion,        the melt is agitated by agitating elements after the cooling means, in the direction of flow,        the temperature profile of the glass melt from the melting region up to the overflow is set such that in the melting region, going out from the refining bench, a surface flow of the glass is brought about in the direction toward the loading opening, and in the refining region, in the constriction, and in the conditioning region a surface flow of the glass in the direction toward the overflow is brought about, a flow only in the direction toward the overflow being brought about above the refining bench,        the flow cross-section of the glass melt is reduced between the melting region and the conditioning region,        the reduction of the flow cross-section is carried out in stepped fashion,        the oxidants for the combustion of the fuels are preheated,        the preheating of the oxidants is carried out in regenerator blocks,        the melting device is operated in a cross-flame method, and the oxidants are introduced from the regenerator blocks through burner ports into the melting region, and/or        the fuels are supplied to burners situated underneath the burner ports, and the flames are directed into the gas chamber above the glass melt.        
The use of the method and device are particularly advantageous for the production of flat glass and of panels for solar elements.